The synthesis of N-ethyl-n-butylamine by amines disproportionation

Article abstract of DOI:10.1007/s11164-012-0790-8

A synthesis of N-ethyl-n-butylamine with simple separation method in a fixed-bed reactor using CuO-NiO-PtO/γ-Al₂O₃ as the catalyst was proposed and investigated. The present catalytic system gave high activity and good selectivity, and the reaction conditions such as temperature and liquid hourly space velocity were optimized. Since no water was generated, the protocol proved to be easy to separate, and N-ethyl-n-butylamine was collected at 110 °C by distillation. The yield and the purity were 60.7 and 99.5 %, respectively.

Full text of DOI:10.1007/s11164-012-0790-8

Res Chem Intermed (2013) 39:2697–2704
DOI 10.1007/s11164-012-0790-8
The synthesis of N-ethyl-n-butylamine by amines
disproportionation
•
Lu-feng Xu Jia-min Huang Chao Qian
•
•
•
•
•
Xin-zhi Chen Lie Feng Yun-bin Chen
Chao-hong He
Received: 3 May 2012 / Accepted: 23 August 2012 / Published online: 7 September 2012
Ó Springer Science+Business Media B.V. 2012
Abstract A synthesis of N-ethyl-n-butylamine with simple separation method in a
fixed-bed reactor using CuO–NiO–PtO/c-Al2O3 as the catalyst was proposed and
investigated. The present catalytic system gave high activity and good selectivity,
and the reaction conditions such as temperature and liquid hourly space velocity
were optimized. Since no water was generated, the protocol proved to be easy to
separate, and N-ethyl-n-butylamine was collected at 110 °C by distillation. The
yield and the purity were 60.7 and 99.5 %, respectively.
Keywords N-Ethyl-n-butylamine Á Disproportionation Á Fixed-bed reactor Á
Catalyst
Introduction
N-Ethyl-n-butylamine is an important pesticide and pharmaceutical intermediate,
which can be used for the synthesis of herbicides, such as pebulate and benfluralin
L. Xu Á J. Huang Á C. Qian Á X. Chen Á C. He
State Key Laboratory of Chemical Engineering, Zhejiang University, Hangzhou,
People’s Republic of China
L. Xu Á J. Huang Á C. Qian Á X. Chen (&) Á C. He
Department of Chemical and Biological Engineering, Zhejiang University,
Hangzhou 310027, People’s Republic of China
e-mail: xzchen@zju.edu.cn
L. Xu
College of Chemical and Materials Engineering, Quzhou College, Quzhou 324000,
People’s Republic of China
L. Feng Á Y. Chen
Zhejiang Jianye Chemical Co., Ltd., Hangzhou 311600, People’s Republic of China
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[1], and the synthesis of nervous system drugs, such as milnacipran [2]. There are
many methods for the synthesis of N-ethyl-n-butylamine, and the most commonly
used method is N-alkylation of amine with aryl/alkyl halides [3, 4]. However, the
use of aryl/alkyl halides is unfriendly to the environment, and this procedure
generates large amounts of inorganic salts as byproducts [5]. The relatively green
method for the synthesis of N-ethyl-n-butylamine is the catalytic amination of
alcohols [6–8], generally by using the Cu, Ni, and Co catalysts. However, this
method generates water as a byproduct, which will reduce the activity of the catalyst
and may form azeotrope with the raw material alcohol and the product amine, thus
rendering the purification of the target product difficult.
The process for the amines disproportionation is a class of common side reactions
in the synthesis of aliphatic amines. Some researchers have studied the amines
disproportionation phenomenon in a number of systems, trying to suppress the
disproportionation to improve the selectivity of primary products; however, the results
showed that preventing the amines disproportionation reactions from the source was
very difficult, and only possible by reducing the activity of the catalyst to reduce the
amines disproportionation [7, 9, 10]. The research of the amines disproportionation
reaction as the main reaction is small and the cross-disproportionation of a variety of
aliphatic amines to synthesize asymmetric amines, such as the synthesis of N-ethyl-n-
butylamine from ethylamine and butylamine, is even rarer. An earlier study of the
conversion between methylamine, dimethylamine, and trimethylamine was carried
out, and the result showed either methylamine or dimethylamine as the raw material,
and a mixture of methylamine, dimethylamine, and trimethylamine was found [11,
12]. The catalysts of the amines disproportionation are mainly metal or supported
metal catalysts, and one having high catalytic activity and acidic centers would be
favorable to the amines disproportionation reaction. Many transition metals have been
used in the amines disproportionation reaction, such as Ni, Cu, Co, Ru, Pt, or Pd [7],
among which Ni has high catalytic activity [8, 13–15]. The acidic centers of catalyst
are often provided by the support, and the performance of the catalyst alters with
changing the catalyst’s acidity. A specific study on the role of the support on the
properties of Cu–Cr catalysts has been reported [16], and the result showed that the
performance varied in the following order, SiO2–Al2O3 & Al2O3 [ SiO2 & graph-
ite & ZnO.
In this paper, we report on the synthesis of N-ethyl-n-butylamine from ethylamine
and butylamine with CuO–NiO–PtO/c-Al2O3 catalyst in a fixed-bed reactor. A
report on a photocatalytic process of N-alkylation of different amines by using
microreactors with immobilized Pt-free TiO2 as well as Pt-loaded TiO2 can be found
in the literature [17]. The N-ethylation process of butylamine was examined in the
ethanol solvent with immobilized Pt-loaded TiO2 and found to yield only 36 %.
There was another report [18] on the synthesis of N-ethyl-n-butylamine, and the
yield of the reaction of butylamine and ethanol catalyzed by Ni–Sn/Al2O3 was only
42 %. The yield of N-ethyl-n-butylamine in this paper is significantly higher than the
results in the literature. The synthesis of N-ethyl-n-butylamine from ethylamine and
butylamine has an important advantage: the reaction does not generate water, which
solved the fundamental problem of removing the water from the reaction mixture,
and no azeotrope in the reaction mixture made the separation process simple.
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The synthesis of N-ethyl-n-butylamine
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Result and discussions
The synthesis of N-ethyl-n-butylamine was catalyzed by CuO–NiO–PtO/c-Al2O3
through the disproportionation. Starting with ethylamine and butylamine, a mixture
of N-ethyl-n-butylamine, ethylamine, diethylamine, butylamine, dibutylamine, N,
N-diethylbutylamine and some other heavy constituents resulted through the reactions.
The reaction formula of the synthesis of N-ethyl-n-butylamine is as follows:
N
+
NH
3
+
NH
H N
2
2
H
The reaction formula of main byproducts is as follows:
N
2
2
+
NH
H N
3
2
H
N
H
+
NH
NH
3
2
The reaction formula of minor byproducts is as follows:
NH3
+
+
N
H
H2N
N
+
+
NH
3
N
H
NH
2
N
2
NH
+
3
3
H N
2
3
N
N
2
NH
3
+
NH
2
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L. Xu et al.
100
80
60
40
20
0
Conversiona
Selectivityb
140
160
180
200
220
T/ oC
Fig. 1 The influence of temperature on the reaction
The existence of subsidiary reaction brought some byproducts. However, these
byproducts have a certain commercial value; for example, although the demand of
N,N-diethylbutylamine and N,N-dibutylethylamine is low, the value is high, and this
system exactly meets this requirement.
The reaction of ethylamine with butylamine was carried out over CuO–NiO–PtO/
c-Al2O3 in the temperature range of 140–220 °C. Figure 1 shows the influence of
temperature on the reaction at a 2:1 mol ratio of ethylamine to butylamine, 0.2 h-1
liquid hourly space velocity (LHSV), and 0.8 MPa. The conversion of butylamine
increased markedly as the temperature increased and reached a maximum at 200 °C,
while the selectivity of N-ethyl-n-butylamine decreased at over 180 °C. In the
research, 200 °C produced the maximum yield of N-ethyl-n-butylamine. During the
research, the yield of diethylamine, dibutylamine, and N-ethyl-n-butylamine showed
a significant increase from 140 to 180 °C. When the temperature varied from 180 to
200 °C, the increased conversion of butylamine mainly contributed to the increase
of N,N-diethylbutylamine and N,N-dibutylethylamine, which resulted in the decline
of the selectivity. In addition, when the temperature was beyond 200 °C, the
conversion changed slightly, while the selectivity had a relatively evident decrease.
(a) The conversion of butylamine.
moles of product
moles of butylamine converted
(b) Selectivity =
The reaction is also strongly influenced by the LHSV, because low LHSV
prolongs the contact time with the catalyst, promoting further reactions. On the
other hand, at high LHSV, the contact time is too short to convert the raw materials
completely. The results of the influence of LHSV on the reaction are shown in
Fig. 2. The conversion of butylamine decreased markedly as LHSV increased,
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The synthesis of N-ethyl-n-butylamine
2701
95
90
85
80
75
70
65
60
55
50
45
40
35
30
25
20
15
10
5
Butylaminea
N-ethyl-n-butylamineb
N,N-diethylbutylaminec
N,N-dibutylethylaminec
Dibutylamineb
0
0.05
0.10
0.15
0.20
0.25
0.30
0.35
LHSV/h-1
Fig. 2 The influence of LHSV on the reaction
especially beyond 0.2 h-1. When the contact time was short, it was favorable for
generating N-ethyl-n-butylamine and dibutylamine, while at the long contact time, it
was favorable for getting N,N-diethylbutylamine and N,N-dibutylethylamine. In the
research, LHSV of 0.2 h-1 resulted in the highest yield of N-ethyl-n-butylamine.
(a) The conversion of butylamine.
(b) The selectivity of N-ethyl-n-butylamine and dibutylamine.
(c) Ten times the selectivity of N,N-diethylbutylamine and N,N-dibutylethylamine.
Moreover, the influence of catalyst at the optimum condition (ethylamine and
butylamine at a 2:1 mol ratio, 200 °C temperature, 0.2 h-1 LHSV, and 0.8 MPa
pressure.) was also explored and the results are summarized in Table 1. Catalytic
activity of CuO–alumina was low, while NiO–alumina showed high disproportion-
ation activity but poor selectivity due to further reaction and due to deamination
[19]. In addition, copper proved to be an unstable catalyst and needed different
Table 1 The effect of different catalyst on the reaction
Catalysta
Butylamine conversion (%)
N-Ethyl-n-butylamine selectivity (%)
CuO/c-Al2O3
CuO–NiO/c-Al2O3
CuO–NiO–PtO/c-Al2O3
NiO/c-Al2O3
a
21.5
87.6
92.6
98.2
26.4
56.5
65.6
15.2
The supported metal content of CuO/c-Al2O3, NiO/c-Al2O3 and CuO–NiO/c-Al2O3 was equal to the
CuO–NiO–PtO/c-Al2O3 catalyst, and the proportion of copper and nickel in the CuO–NiO/c-Al2O3
catalyst was also equal to the proportion in the CuO–NiO–PtO/c-Al2O3 catalyst
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additives to stabilize the copper catalyst. Therefore, CuO–NiO–PtO/c-Al2O3 was
selected as the catalyst. The ratio of copper and nickel was also investigated, and too
low a nickel content made the catalytic activity poor, while too high a nickel content
lowered the selectivity. Platinum was added to improve the catalytic activity and
selectivity.
Conclusions
In conclusion, an easy separation method for the synthesis of N-ethyl-n-butylamine
from ethylamine and butylamine by amine disproportionation was examined in a
fixed-bed reactor in the presence of CuO–NiO–PtO/c-Al2O3 as the catalyst. During
the research, the optimum temperature and LHSV were investigated. Moreover, the
catalyst was also explored and CuO–NiO–PtO/c-Al2O3 we selected gave high
activity and good selectivity.
Experimental
The CuO–NiO–PtO/c-Al2O3 catalyst was prepared using an impregnation method at
fixed Cu/Ni/Pt ratio, and concrete steps are as follows:
(a) The carrier c-Al2O3 (SBET = 200–220 m2 g-1, U = 2–3 mm) was calcined
for 3 h at 450 °C and for 5 h at 650 °C in muffle furnace.
(b) The calcined c-Al2O3 was impregnated with water for 36 h, then measured the
decrement of water volume to determine the pore volume.
(c) The solution of copper nitrate, nickel nitrate, and platinum nitrate was prepared
to obtain Cu, Ni, and Pt concentrations of 11.2, 8.6, and 0.9 wt%, respectively,
and the volume of the solution was two times the total pore volume. Then, the
calcined c-Al2O3 from (a) was impregnated with the above-mentioned solution
for 36 h, filtrated, and dried at 60 °C for 2 h, and the filtrate was collected at
the same time.
(d) The filtrated catalyst was calcined at 280 °C for 6 h in a muffle furnace, and
then cooled.
(e) After cooling, the catalyst was impregnated with filtrate from (c) for 24 h, then
dried at 80 °C.
(f) Finally, the catalyst was calcined at 450 °C for 6 h, and then cooled to room
temperature.
The reaction was performed in a stainless reactor tube filled with the catalyst and
surrounded by a jacket filled with a salt bath to control the temperature of the fixed-
bed. The total height of the reactor was 60 cm, the effective length was 40 cm, and
ceramic rings were placed on the top and at the bottom. The effective radius of the
reactor was 15 mm. The fixed-bed reactor is shown in Fig. 3. All reactions were
carried out under an atmosphere of hydrogen in a fixed-bed, which was filled with
105 cm3 of the calcinated catalyst, and the catalyst was reduced at 230 °C for 8 h
before reaction.
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The synthesis of N-ethyl-n-butylamine
2703
Vaporization
Catalyst
Raw material
Heating jacket
Hydrogen
Condenser
Discharge
Fig. 3 The fixed-bed reactor
Ethylamine (730 g, 16.2 mol) and butylamine (592 g, 8.1 mol) were evenly
mixed in the reservoir and were introduced at the top of the reaction tube via an
injection pump. The raw material passed through the catalyst in the fixed-bed at
200 °C, 0.2 h-1 LHSV, and 0.8 MPa pressure, and the gas products were cooled
down after passing through the cooling rings at the bottom.
The reaction mixtures were separated by distillation. During the distillation, the
heating quantity of the kettle was adjusted to control the steam flow, and the top
temperature was monitored to obtain different distillates. N-ethyl-n-butylamine was
collected at 110 °C (497.8 g, 60.7 % yield, and 99.5 % GC purity).
The distillate was analyzed by gas chromatography (Agilent 1790F and SE-30
column) and GC–MS (TRACE GC2000/TRACE MS).
Acknowledgments This work was supported by the National Natural Science Foundation of China (No.
21006087), the Natural Science Foundation of the Zhejiang Province (Y4100147, Y4100544), the
Science and Technology Research Fund of Quzhou City (20101056), the Fundamental Research Funds
for the Central Universities (2011QNA4018), and the Key Innovation Group of Zhejiang Province
(2009R50002).
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